1. Field of the Invention
The present invention relates to image reading apparatuses and methods of controlling the apparatuses.
2. Description of the Related Art
Image reading apparatuses are known that are equipped with automatic document feeders (ADFs). Some of these image reading apparatuses are provided with a flowing document reading mode in which originals that are fed from the ADF are read while being conveyed at a fixed velocity in a state where a scanning unit that irradiates light onto the originals is secured. Since it is sufficient for the originals to be fed in one direction at a fixed velocity, this flowing document reading mode has an advantage compared to a case where originals are read with the originals being in a fixed state while the scanning unit moves in that the intervals between reading times of the originals can be shortened.
When a foreign substance such as dust or dirt adheres to the reading position of originals in a case of this flowing document reading mode, the foreign substance is detected as all black pixels in the reading scan. There is a problem with these black pixels in that they appear as black streaks in the sub scanning direction (a feeding direction of the original) of the image that has been read, and they conspicuously reduce the quality of the image that has been obtained by reading the documents.
As a method of addressing this generation of black streaks, Japanese Patent Laid-Open No. 2001-144901 describes an image reading apparatus that is provided with a means for detecting the generation of black streaks whose generation originates in dust or dirt on the platen glass, and that executes dust detection on the image data obtained by the reading. In a case where it is determined that dust or dirt is adhering, the image reading apparatus uses multiple adjacent pixel data to correct the pixel data corresponding to the portion of image data obtained by reading in which dust or dirt was detected.
When the aforementioned dust detection is carried out using a line memory, hardware circuitry such as a line memory is necessary. To eliminate the addition of such circuitry, it is also possible to execute the dust detection on the main memory and the CPU without using a line memory. However, in that case the load on the CPU is increased such that the processing speed of the CPU decreases, and therefore there is a problem of being unable to support high-speed original reading operations.